Chemical mechanical polishing (also known as chemical mechanical planarization or CMP) is a semiconductor manufacturing process that uses an abrasive, corrosive slurry in conjunction with a polishing pad to planarize the microscopic topographic features on a partly processed wafer so that subsequent processes can begin from a flat surface. CMP is also used in damascene processes to define features, such as interconnects and vias. The planarization process relies on both physical grinding as well as chemical reactions that often occur between the material being polished and components of the slurry.
The abrasive particles within a CMP slurry tend to agglomerate over time, even during storage at room temperatures. The quality of a CMP slurry therefore deteriorates as it ages. This agglomeration of abrasive particles diminishes the quality of the resulting polish by affecting the polish uniformity and increasing the wafer defect rate. Furthermore, a CMP slurry is subjected to high shearing during a CMP process due to the rotation of the polishing pad and wafers and due to the small gap between the pad and the wafer. This shearing can irreversibly change slurry properties and also affect CMP performance.
It would be advantageous to develop a process by which the age of a CMP slurry can be determined, thereby allowing aged slurries to be discarded before they affect the quality of a wafer polishing process. The current state of the art viscosity metrology does not detect particle agglomeration.